This invention relates generally to a bush cutting apparatus, and more particularly to an improved brake mechanism for stopping rotation of a cutter blade of a bush cutting apparatus.
Brake mechanisms of bush cutting apparatuses are known, for example, from Japanese Utility Model Laid-Open Publication Nos. 51-53248 and 51-99039. The first-mentioned 51-53248 publication discloses a bush cutting apparatus which includes brake shoes and cam plates for moving the brake shoes into and out of engagement with a driven shaft. As a human operator releases a brake bar, the cam plates are caused, via springs, to pivot to press the brake shoes against the driven shaft, so that there is automatically produced a braking force to stop rotation of the rotary cutter.
The second-mentioned 51-99039 publication discloses a bush cutting apparatus which includes a brake lining provided along the outer periphery of a clutch drum. As a human operator releases a lever, the brake lining comes into engagement with the outer periphery of the clutch drum and a signal is generated from a movable contact to deactivate a prime mover or drive source, so that a rotary cutter can be caused to stop its rotation.
With the structure disclosed in the 51-53248 publication, it would take a considerable deal of time and labor to deactivate the rotary cutter because the human operator is required to manually manipulate the brake lever. Further, the disclosed structure requires a great number of component parts, such as the brake lever, wires and the like and hence add to production costs.
Also, with the structure disclosed in the 51-99039 publication, it would take a considerable deal of time and labor to deactivate the drive source and rotary cutter because the human operator is required to manually manipulate the lever, which leads to a poor operability. Further, in the disclosed bush cutting apparatus, a control rod coupled to one end of a connecting wire extends through a hole formed in a clutch housing, and measures for maximizing dust-tightness and water-tightness must be taken in relation to the hole in the clutch housing. Furthermore, extra operations are necessary for checking and adjusting the tension of the connecting wire coupled at the other end to the lever, which would require an extra time and labor.
In view of the foregoing, it is an object of the present invention to provide an improved bush cutting apparatus which can achieve an enhanced operability and enhanced dust-tightness and water-tightness and which can be manufactured at reduced costs.
According to one embodiment of the present invention, there is provided an improved bush cutting apparatus of the type which includes a cutter-blade driving shaft having a cutter blade attached thereto and a drive source having an output shaft operatively connected with the cutter-blade driving shaft for rotating the cutter-blade driving shaft via a clutch mechanism and a brake mechanism. The clutch mechanism in the bush cutting apparatus of the invention comprises: a rotating member mounted on the output shaft of the drive source; a clutch moving member mounted on the rotating member for sliding movement along a radial direction of the rotating member, the clutch moving member having a tapered outer side surface; a clutch drum mounted on the cutter-blade driving shaft for axial movement therealong and having a tapered portion with an inner surface corresponding in contour to the tapered outer side surface of the clutch moving member; and a clutch resilient member for normally pulling the clutch moving member toward an axial centerline of the rotating member. The brake mechanism comprises: a brake shoe formed at a tip of an open end portion of the clutch drum that constitutes a greatest diameter region of the tapered portion in the clutch drum; a brake pad secured to a non-rotating fixed housing in opposed relation to the brake shoe; and a braking resilient member for normally pressing the brake shoe against the brake pad. When the rotating member is not rotated by the drive source at more than a predetermined rotation speed, the clutch moving member is kept disengaged from the clutch drum due to pulling force of the clutch resilient member so that the brake shoe is pressed against the brake pad to apply the brakes. But, when the rotating member is rotated by the drive source at more than a predetermined rotation speed, the clutch moving member is moved radially outward to press the clutch drum by centrifugal force in such a manner that the clutch drum is caused, by the tapered outer side surface of the clutch moving member, to slide to a non-braking position.
When the rotation of the rotating member and hence of the cutter blade has fallen below the predetermined rotation speed, the brake mechanism is automatically activated to terminate the rotation of the cutter blade. Namely, when the number of rotations of the drive source and hence of the clutch mechanism has fallen below a predetermined value, the moving member in the clutch mechanism is disengaged from the clutch drum, and thus the clutch drum is freed and resiliently slid, by the brake mechanism, back to a predetermined braking position where the brake shoe is pressed against the brake pad to apply the brakes; namely, in this case, the brake mechanism causes the brake shoe to be pressed against the brake pad via the braking resilient member. As a result, the clutch drum having the brake shoe as well as the cutter-blade driving shaft and the cutter blade is caused to stop rotating. Because the brake mechanism is thus automatically activated in accordance with a variation in the number of rotations of the drive source, the present invention can eliminate the need for a human operator to manually manipulate a brake lever or the like, and thus allows the human operator to manipulate the bush cutting apparatus with a significantly enhanced operability.
On the other hand, when the number of rotations of the drive source and hence of the clutch mechanism has increased above a predetermined value, the clutch moving member in the clutch mechanism is caused to slide radially outward along the rotating member in such a manner that the clutch moving member slides the clutch drum to the non-braking position against the bias of the braking resilient member while transmitting the rotational force from the rotating member to the clutch drum by means of the tapered outer side surface, so that the brake shoe formed on the clutch drum is disengaged from the brake pad to release the brakes.
With such arrangements, the present invention can dispense with a lever and wire for braking operation by the human operator and eliminate a need for an apparatus housing to have a hole for passing component parts, such as a wire and rod, through the housing. As a result, the present invention can achieve enhanced dust-tightness and water-tightness of the bush cutting apparatus. Further, because the parts, such as the brake lever and wire, can be dispensed with, the bush cutting apparatus of the present invention can be manufactured at reduced costs.
According to another embodiment of the present invention, there is provided another improved bush cutting apparatus of the type including a cutter-blade driving shaft having a cutter blade attached thereto and a drive source having an output shaft operatively connected with the cutter-blade driving shaft for rotating the cutter-blade driving shaft via a clutch mechanism and brake mechanism. In this bush cutting apparatus, the clutch mechanism comprises: a rotating member mounted on the output shaft of the drive source; a clutch moving member mounted on the rotating member for movement along radial and axial directions of the rotating member; a clutch drum mounted on the cutter-blade driving shaft for axial movement therealong; and a clutch resilient member for normally pulling the clutch moving member toward an axial centerline of the rotating member. The brake mechanism comprises: a brake shoe formed at a tip of an open end portion of the clutch drum; a brake pad secured to a non-rotating fixed housing in opposed relation to the brake shoe; and a braking resilient member for normally pressing the brake shoe against the brake pad. When the rotating member is not rotated by the drive source at more than a predetermined rotation speed, the clutch moving member is kept disengaged from the clutch drum due to pulling force of the clutch resilient member in such a manner that the brake shoe is pressed against the brake pad to apply the brakes, while when the rotating member is rotated by the drive source at more than a predetermined rotation speed, the clutch moving member is moved radially outward and axially to press and slide the clutch drum in a direction where the brake shoe is disengaged from the brake pad.
When the number of rotations of the drive source and hence of the clutch mechanism has fallen below a predetermined value in the other embodiment, the moving member in the clutch mechanism is disengaged from the clutch drum, and thus the clutch drum is freed and resiliently slid, by the brake mechanism, back to a predetermined braking position where the brake shoe is pressed against the brake pad to apply the brakes; namely, the brake mechanism causes the brake shoe to be pressed against the brake pad via the braking resilient member. As a result, the clutch drum having the brake shoe as well as the cutter-blade driving shaft and the cutter blade is caused to stop rotating. Because the brake mechanism is thus automatically activated in accordance with a variation in the number of rotations of the drive source, the present invention can eliminate the need for a human operator to manually manipulate a brake lever or the like, and thus allows the human operator to manipulate the bush cutting apparatus with a significantly enhanced operability.
On the other hand, when the number of rotations of the drive source and hence of the clutch mechanism has increased above a predetermined value, the clutch moving member in the clutch mechanism is caused not only to slide radially outward along the rotating member but also move in the axial direction away from the brake pad. Such movement of the clutch moving member causes the brake shoe of the clutch drum to disengage from the brake drum, thereby releasing the brakes.
With such arrangements, the present invention can dispense with a lever and wire for braking operation by the human operator and eliminate a need for an apparatus housing to have a hole for passing component parts, such as a wire and rod, through the housing. As a result, the present invention can achieve enhanced dust-tightness and water-tightness of the bush cutting apparatus.
In a preferred embodiment of the present invention, a plurality of the clutch moving members are provided symmetrically with each other about the axial centerline of the rotating member. The symmetrical arrangement can distribute the weights of the moving members and thus can reliably prevent unbalance during the rotation. Further, the symmetrical arrangement permits synchronization between the two moving members and thereby allows the clutch mechanism and brake mechanism to operate smoothly, so that reliable brake performance can be accomplished.